Cathode material and battery

ABSTRACT

Provided is a cathode material including a cathode active material; a coating layer which coats at least a part of a surface of the cathode active material, and which includes a first solid electrolyte material; and a second solid electrolyte material. The first solid electrolyte material includes Li, M, and X; however, does not include sulfur. M includes at least one element selected from the group consisting of metalloid elements and metal elements other than Li. X includes at least one element selected from the group consisting of Cl and Br.

BACKGROUND 1. Technical Field

The present disclosure relates to a cathode material for a battery and abattery.

2. Description of the Related Art

Patent Literature 1 discloses a battery using, as a solid electrolyte, ahalide including indium. Patent Literature 2 discloses an all-solidlithium battery in which a surface of a cathode active material iscoated with a lithium ion conductive oxide having substantially noelectronic conductivity.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Application Publication No.    2006-244734-   Patent Literature 2: Japanese Patent Publication No. 4982866

Non-Patent Literature

-   Non-patent Literature 1: Chem. Mater. 2016, 28, 266-273.

SUMMARY

In the prior art, suppression of an increase in a reaction overvoltageof a battery is desired.

The cathode material according to one aspect of the present disclosurecomprises:

a cathode active material;

a coating layer which coats at least a part of a surface of the cathodeactive material and includes a first solid electrolyte material; and

a second solid electrolyte material,

wherein

the first solid electrolyte material includes Li, M, and X;

the first solid electrolyte material does not include sulfur;

M includes at least one element selected from the group consisting ofmetalloid elements and metal elements other than Li; and

X includes at least one element selected from the group consisting of Cland Br.

According to the present disclosure, the increase in the reactionovervoltage of the battery can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a schematic configuration of acathode material in a first embodiment.

FIG. 2 is a cross-sectional view showing a schematic configuration of abattery in a second embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be describedwith reference to the drawings.

First Embodiment

The cathode material in the first embodiment includes a cathode activematerial, a first solid electrolyte material, and a second solidelectrolyte material.

The first solid electrolyte material is located on a surface of thecathode active material to form a coating layer.

The first solid electrolyte material is a material represented by thefollowing composition formula (1):

Li_(α)M_(β)X_(γ)  Formula (1)

where α, β, and γ are each independently a value greater than zero.

M includes at least one element selected from the group consisting ofmetalloid elements and metal elements other than Li.

X includes at least one element selected from the group consisting of Cland Br.

According to the above configuration, an increase in a reactionovervoltage of a battery can be suppressed.

Patent Literature 1 discloses that, in the all-solid secondary batteryincluding a solid electrolyte consisting of a compound including indium,it is preferable that the cathode active material has an electricpotential with regard to Li of not more than 3.9 V on average, and thatthereby a film consisting of a decomposition product due to oxidativedecomposition of the solid electrolyte is formed to provide a goodcharge/discharge characteristic. In addition, a general layeredtransition metal oxide cathode such as LiCoO₂ orLiNi_(0.8)Co_(0.15)Al_(0.05)O₂ is disclosed as the cathode activematerial having an electric potential with regard to Li of not more than3.9 V on average.

On the other hand, as a result of intensive studies by the presentinventors, the present inventors found that, in a battery using a halidesolid electrolyte including iodine (=I) in a cathode material (namely,one example of the second solid electrolyte material), even if a cathodeactive material having an electric potential with regard to Li of notmore than 3.9 V is used, the halide solid electrolyte is oxidized anddecomposed during charge. In addition, the present inventors presumedthat there arises a problem that a reaction overvoltage of the batteryis increased together with the oxidation and decomposition, and that thereason therefor is an oxidation reaction of iodine included in thehalide solid electrolyte. Specifically, in addition to a normal chargingreaction in which lithium and electrons are extracted from the cathodeactive material in the cathode material, a side reaction in whichelectrons are also extracted from the halide solid electrolyte includingiodine in contact with the cathode active material occurs. In otherwords, an oxidative decomposition layer having poor lithium-ionconductivity is formed between the cathode active material and thehalide solid electrolyte, and the oxidative decomposition layerfunctions as a large interface resistance in the electrode reaction ofthe cathode. In order to solve this problem, it is necessary to suppresselectron transfer to the halide solid electrolyte including iodine tosuppress the formation of the oxidative decomposition layer.

Non-patent Literature 1 discloses calculation results regarding electricpotential stability of various solid electrolytes such as an oxide solidelectrolyte, a sulfide solid electrolyte, and a halide solidelectrolyte. With regard to the halide solid electrolyte, it has beendisclosed that the electric potential stability thereof varies dependingon the anion species forming the halide solid electrolyte. For example,it has been disclosed that a halide solid electrolyte including Br hasan electric potential stability of not more than 4.0 V vs. Li.

On the other hand, as a result of intensive studies by the presentinventors, the present inventors found that, even if solid electrolyteshave an upper limit of the electric potential stability derived fromcalculation of less than 4.0 V vs. Li, some of the solid electrolytesexhibit the stable charge/discharge characteristic if used for a cathodematerial. For example, if a halide solid electrolyte which includesbromine and has an upper limit of the electric potential stability ofnot more than 4.0 V vs. Li is used for the cathode material, the halidesolid electrolyte exhibits a good charge/discharge characteristic evenif charge is performed at a voltage of not less than 4.0 V vs. Li. Onthe other hand, the present inventors found that, if a halide solidelectrolyte including iodine is used for the cathode material,charge/discharge efficiency is lowered significantly. Although detailsof the mechanism thereof are not clear, if the halide solid electrolyteincluding bromine is used for the cathode material, the solidelectrolyte is oxidized during the charge in the immediate vicinitywhere the cathode active material and the solid electrolyte are incontact with each other. However, since the electronic conductivity ofthe oxidation product is significantly low, the reaction does notproceed continuously into the solid electrolyte. On the other hand, ifthe halide solid electrolyte including iodine is used for the cathodematerial, the oxidation product of the solid electrolyte has electronicconductivity. As a result, the reaction is not retained only in thevicinity where the cathode active material and the solid electrolyte arein contact with each other, the reaction proceeds continuously into thesolid electrolyte, and the oxidative decomposition layer of the solidelectrolyte is formed continuously. As a result, it is conceivable thatthe reaction overvoltage of the battery is increased. As describedabove, the battery operation when the solid electrolyte is used for thecathode material cannot be estimated only from the calculation resultdisclosed in Non-patent Literature 1.

Since a halide solid electrolyte including iodine has poor oxidationstability, the oxidative decomposition occurs continuously during thecharge in a battery in which the cathode active material and the halidesolid electrolyte including iodine are in contact with each other. Onthe other hand, the halide solid electrolyte which does not includeiodine (namely, one example of the first solid electrolyte material) isexcellent in oxidation stability. Even if the halide solid electrolytewhich does not include iodine is brought into direct contact with thecathode active material, the oxidative decomposition does not occur, ora reaction does not continue even if the oxidative decomposition occurs.In the configuration according to an embodiment of the presentdisclosure, the cathode active material and the halide solid electrolyteincluding iodine are separated by a coating layer including the halidesolid electrolyte which does not include iodine, and are not in directcontact with each other. Therefore, according to the aboveconfiguration, the oxidation of the halide solid electrolyte includingiodine can be suppressed, and the increase in the reaction overvoltageof the battery can be suppressed. In addition, the halide solidelectrolyte including iodine is superior in ion conductivity to thehalide solid electrolyte which does not include iodine. Therefore,according to the above configuration, an output characteristic of thebattery can be further improved, as compared with a case where only thehalide solid electrolyte which does not include iodine is used for acathode layer.

The halide solid electrolytes have high ion conductivity and excellentthermal stability, and do not generate a harmful gas such as hydrogensulfide. Therefore, by using the halide solid electrolyte, the outputcharacteristic and the thermal stability of the battery can be improved,and the generation of the harmful gas such as hydrogen sulfide can besuppressed.

Patent Literature 2 discloses that a high resistance layer is formed bycontact between a sulfide solid electrolyte and a cathode activematerial that exhibits a redox reaction at an electric potential of notless than 3 V, and that the formation of the high resistance layer canbe suppressed by coating a surface of the cathode active material with alithium ion conductive oxide having no electronic conductivity.

Here, the present inventors found an idea that the high resistance layerwould be allowed to be suppressed by coating the cathode active materialwith a lithium ion conductive halide having no electronic conductivity.Furthermore, by coating the cathode active material with a halide solidelectrolyte that is superior in lithium ion conductivity to an oxidesolid electrolyte, Li transfer resistance from the solid electrolyte tothe cathode active material is allowed to be suppressed.

As already described, Patent Literature 1 discloses that, in theall-solid secondary battery including a solid electrolyte consisting ofa compound including indium, it is preferable that the cathode activematerial has an electric potential with regard to Li of not more than3.9 V on average, and that thereby a film consisting of a decompositionproduct due to oxidative decomposition is formed to provide a goodcharge/discharge characteristic. However, detailed mechanism of theoxidative decomposition is not clarified.

As a result of intensive studies by the present inventors, the presentinventors found that, in a case where iodine is included in the halidesolid electrolyte, the oxidation reaction proceeds to form a resistancelayer even if a cathode active material having an electric potentialwith regard to Li of not more than 3.9 V on average is used. The presentinventors presumed that an iodine-containing halide solid electrolyte incontact with the cathode active material is oxidized as a side reactionduring the charge to form a resistance layer having poor ionconductivity.

In an all-solid battery that uses a sulfide solid electrolyte (oneexample of the second solid electrolyte material) for the cathode, bycoating the cathode active material with a halide solid electrolyte thatdoes not include iodine (one example of the first solid electrolytematerial), the formation of the high resistance layer due to the contactbetween the cathode active material and the sulfide solid electrolyte issuppressed, and a low resistance cathode active material/sulfide solidelectrolyte interface can be formed due to high ion conductivity of thehalide solid electrolyte.

In a configuration according to another embodiment of the presentdisclosure, electron transfer to the sulfide solid electrolyte issuppressed by the iodine-free halide solid electrolyte included in thecoating layer. As a result, a side reaction of the sulfide solidelectrolyte does not occur, and the charge/discharge efficiency isimproved. Further, since no side reaction occurs, the formation of theoxide layer is suppressed, and interfacial resistance of the electrodereaction can be lowered.

The term “metalloid elements” are B, Si, Ge, As, Sb, and Te.

The term “metal elements” are all elements included in Groups 1 to 12 ofthe periodic table except for hydrogen, and all elements included inGroups 13 to 16 of the periodic table except for B, Si, Ge, As, Sb, Te,C, N, P, O, S, and Se. In other words, the metal element becomes acation if the metal element forms an inorganic compound with a halogencompound.

The halide solid electrolyte including at least one element selectedfrom the group consisting of metalloid elements and metal elements otherthan Li has higher ion conductivity than a halide solid electrolyte suchas LiI composed only of Li and a halogen element. As a result, in a casewhere the halide solid electrolyte including the at least one elementselected from the group consisting of metalloid elements and metalelements other than Li is used for the battery, the outputcharacteristic of the battery can be improved.

In the composition formula (1), M may include Y (=yttrium).

In other words, the first solid electrolyte material may include Y as ametal element.

According to the above configuration, the ion conductivity of the firstsolid electrolyte material can be further improved. Thereby, thecharge/discharge characteristic of the battery can be further improved.

The first solid electrolyte material including Y may be, for example, acompound represented by a composition formula of Li_(a)Me_(b)Y_(c)X₆.Here, a+mb+3c=6 andc>0 are satisfied. Me is at least one selected fromthe group consisting of metalloid elements and metal elements other thanLi and Y. The value of m is a valence of Me.

As Me, at least one element selected from the group consisting of Mg,Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb may be used.

According to the above configuration, the ion conductivity of the firstsolid electrolyte material can be further improved.

In the composition formula (1), 2.5≤α≤3, 1≤β≤1.1, and γ=6 may besatisfied.

According to the above configuration, the ion conductivity of the firstsolid electrolyte material can be further improved. Thereby, thecharge/discharge characteristic of the battery can be further improved.

The first solid electrolyte material may be a material represented bythe following composition formula (A1):

Li_(6-3d)Y_(d)X₆  Formula (A1)

where, in the composition formula (A1), X is at least one elementselected from the group consisting of Cl and Br. In the compositionformula (A1), 0<d<2 is satisfied.

According to the above configuration, the ion conductivity of the firstsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

The first solid electrolyte material may be a material represented bythe following composition formula (A2):

Li₃YX₆  Formula (A2)

where, in the composition formula (A2), X is at least one elementselected from the group consisting of Cl and Br.

According to the above configuration, the ion conductivity of the firstsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

The first solid electrolyte material may be a material represented bythe following composition formula (A3):

Li_(3-3δ)Y_(1+δ)Cl₆  Formula (A3)

where, in the composition formula (A3), 0<δ≤0.15 is satisfied.

According to the above configuration, the ion conductivity of the firstsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

The first solid electrolyte material may be a material represented bythe following composition formula (A4):

Li_(3-3δ)Y_(1+δ)Br₆  Formula (A4)

where, in the composition formula (A4), 0<δ≤0.25 is satisfied.

According to the above configuration, the ion conductivity of the firstsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

The first solid electrolyte material may be a material represented bythe following composition formula (A5):

Li_(3-3δ+a)Y_(1+δ-a)Me_(a)Cl_(6-x)Br_(x)  Formula (A5)

where, in the composition formula (A5), Me is one or more kinds ofelements selected from the group consisting of Mg, Ca, Sr, Ba, and Zn.

In the composition formula (A5), −1<δ<2, 0<a<3, 0<(3−3δ+a), 0<(1+δ−a),and 0≤x≤6 are satisfied.

According to the above configuration, the ion conductivity of the firstsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

The first solid electrolyte material may be a material represented bythe following composition formula (A6):

Li_(3-3δ)Y_(1+δ-a)Me_(a)Cl_(6-x)Br_(x)  Formula (A6)

where, in the composition formula (A6), Me is one or more kinds ofelements selected from the group consisting of A1, Sc, Ga, and Bi.

In the composition formula (A6), −1<δ<1, 0<a<2, 0<(1+δ−a), and 0≤x≤6 aresatisfied.

According to the above configuration, the ion conductivity of the firstsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

The first solid electrolyte material may be a material represented bythe following composition formula (A7):

Li_(3-3δ-a)Y_(1+δ-a)Me_(a)Cl_(6-x)Br_(x)  Formula (A7)

where, in the composition formula (A7), Me is one or more kinds ofelements selected from the group consisting of Zr, Hf, and Ti.

In the composition formula (A7), −1<δ<1, 0<a<1.5, 0<(3−3δ−a), 0<(1+δ−a),and 0≤x≤6 are satisfied.

According to the above configuration, the ion conductivity of the firstsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

The first solid electrolyte material may be a material represented bythe following composition formula (A8):

Li_(3-3δ-2a)Y_(1+δ-a)Me_(a)Cl_(6-x)Br_(x)  Formula (A8)

where, in the compositional formula (A8), Me is one or more kinds ofelements selected from the group consisting of Ta and Nb.

In the composition formula (A8), −1<δ<1, 0<a<1.2, 0<(3−3δ−2a),0<(1+δ−a), and 0≤x≤6 are satisfied.

According to the above configuration, the ion conductivity of the firstsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

As the first solid electrolyte material, for example, Li₃YX₆, Li₂MgX₄,Li₂FeX₄, Li(Al, Ga, In)X₄, or Li₃(Al, Ga, In)X₆ may be used. Here, Xincludes at least one element selected from the group consisting of Cland Br.

The second solid electrolyte material includes a material having highion conductivity. For example, a halide solid electrolyte includingiodine is used as the second solid electrolyte material. For example, asthe halide solid electrolyte including iodine, a compound represented bythe following composition formula (2) may be used:

Li_(α′)M′_(β′)X′_(γ′)  Formula (2)

where α′, β′, and γ′ are each independently a value greater than zero.

M′ includes at least one element selected from the group consisting ofmetalloid elements and metal elements other than Li.

X′ includes I and at least one element selected from the groupconsisting of Cl and Br.

According to the above configuration, the ion conductivity of the secondsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

In the composition formula (2), M′ may include Y.

In other words, the second solid electrolyte material may include Y as ametal element.

According to the above configuration, the ion conductivity of the secondsolid electrolyte material can be further improved. Thereby, thecharge/discharge characteristic of the battery can be further improved.

In the composition formula (2), X′ may include Br (=bromine) andC(=chlorine).

According to the above configuration, the ion conductivity of the secondsolid electrolyte material can be further improved. Thereby, thecharge/discharge characteristic of the battery can be further improved.

The second solid electrolyte material may be a material represented bythe following composition formula (B1):

Li_(6-3d)Y_(d)X₆  Formula (B1)

where, in the composition formula (B1), X is one or more kinds ofhalogen elements including at least I. In addition, in the compositionformula (B1), 0<d<2 is satisfied.

According to the above configuration, the ion conductivity of the secondsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

The second solid electrolyte material may be a material represented bythe following composition formula (B2):

Li₃YX₆  Formula (B2)

where, in the composition formula (B2), X is one or more kinds ofhalogen elements including at least I.

According to the above configuration, the ion conductivity of the secondsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

The second solid electrolyte material may be a material represented bythe following composition formula (B3):

Li_(3-3δ+a)Y_(1+δ-a)Me_(a)Cl_(6-x-y)Br_(x)I_(y)  Formula (B3)

where, in the composition formula (B3), Me is one or more kinds ofelements selected from the group consisting of Mg, Ca, Sr, Ba, and Zn.

In the composition formula (B3), −1<δ<2, 0<a<3, 0<(3−3δ+a), 0<(1+δ−a),0≤x<6, 0<y≤6, and (x+y)<6 are satisfied.

According to the above configuration, the ion conductivity of the secondsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

The second solid electrolyte material may be a material represented bythe following composition formula (B4):

Li_(3-3δ)Y_(1+δ-a)Me_(a)Cl_(6-x-y)Br_(x)I_(y)  Formula (B4)

where, in the compositional formula (B4), Me is one or more kinds ofelements selected from the group consisting of Al, Sc, Ga, and Bi.

In the composition formula (B4), −1<δ<1, 0<a<2, 0<(1+δ−a), 0≤x<6, 0<y≤6,and (x+y)<6 are satisfied.

According to the above configuration, the ion conductivity of the secondsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

The second solid electrolyte material may be a material represented bythe following composition formula (B5):

Li_(3-3δ-a)Y_(1+δ-a)Me_(a)Cl_(6-x-y)Br_(x)I_(y)  Formula (B5)

where, in the composition formula (B5), Me is one or more kinds ofelements selected from the group consisting of Zr, Hf, and Ti.

In the composition formula (B5), −1<δ<1, 0<a<1.5, 0<(3−3δ−a), 0<(1+δ−a),0≤x<6, 0<y≤6, and (x+y)<6 are satisfied.

According to the above configuration, the ion conductivity of the secondsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

The second solid electrolyte material may be a material represented bythe following composition formula (B6):

Li_(3-3δ-2a)Y_(1+δ-a)Me_(a)Cl_(6-x-y)Br_(x)I_(y)  Formula (B6)

where, in the composition formula (B6), Me is one or more kinds ofelements selected from the group consisting of Ta and Nb.

In the composition formula (B6), −1<δ<1, 0<a<1.2, 0<(3−3δ−2a),0<(1+δ−a), 0≤x<6, 0<y≤6, and (x+y)<6 are satisfied.

According to the above configuration, the ion conductivity of the secondsolid electrolyte material can be further improved. Thereby, thecharge/discharge efficiency of the battery can be further improved.

As the second solid electrolyte material, for example, Li₃YX₆, Li₂MgX₄,Li₂FeX₄, Li(Al, Ga, In)X₄, or Li₃(Al, Ga, In)Xe may be used. Here, Xincludes I and at least one element selected from the group consistingof Cl and Br.

A sulfide solid electrolyte may also be used as the second solidelectrolyte material. As the sulfide solid electrolyte, for example,Li₂S—P₂S₅, Li₂S—SiS₂, Li₂S—B₂S₃, Li₂S—GeS₂,Li_(3.25)Ge_(0.25)P_(0.75)S₄, or Li₁₀GeP₂S₁₂ may be used. In addition,LiX, Li₂O, MO_(q), or LipMO_(q) may be added thereto. Here, X is one ormore kinds of elements selected from the group consisting of F, Cl, Br,and I. In addition, M is one or more kinds of elements selected from thegroup consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. In addition, pand q are each independently a natural number.

In the first embodiment, the second solid electrolyte material may be asulfide solid electrolyte. For example, the sulfide solid electrolytemay include lithium sulfide and phosphorus sulfide. For example, thesulfide solid electrolyte may be Li₂S—P₂S₅. Li₂S—P₂S₅ has high ionconductivity and is stable against oxidation and reduction. Therefore,by using Li₂S—P₂S₅, the charge/discharge efficiency of the battery canbe further improved.

The cathode active material includes a material having a property ofoccluding and releasing metal ions (for example, lithium ions). Examplesof the cathode active material include a lithium-containing transitionmetal oxide (e.g., Li(NiCoAl)O₂, Li(NiCoMn)₂, or LiCoO₂), a transitionmetal fluoride, a polyanion material, a fluorinated polyanion material,a transition metal sulfide, a transition metal oxysulfide, and atransition metal oxynitride. In particular, if a lithium-containingtransition metal oxide is used as the cathode active material, costreduction can be performed and an average discharge voltage can beincreased.

In the first embodiment, the cathode active material may be a lithiumnickel-cobalt-manganese oxide. For example, the cathode active materialmay be Li(NiCoMn)O₂.

According to the above configuration, an energy density and thecharge/discharge efficiency of the battery can be further increased.

As the first solid electrolyte material included in the coating layer, amaterial having low electron conductivity and resistance againstoxidation may be used. For example, a halide solid electrolyte whichdoes not include iodine may be used as the first solid electrolytematerial.

A halide solid electrolyte which does not include iodine has high ionconductivity and high potential stability. As a result, by using thehalide solid electrolyte that does not include iodine, thecharge/discharge efficiency of the battery can be further increased, andthe increase in the reaction overvoltage of the battery can be furthersuppressed.

In the first embodiment, the first solid electrolyte material may beLi_(2.7)Y_(1.1)Cl₆, Li₃YBr₆, or Li_(2.5)Y_(0.5)Zr_(0.5)Cl₆.

According to the above configuration, the charge/discharge efficiency ofthe battery can be further increased, and the increase in the reactionovervoltage of the battery can be further suppressed.

FIG. 1 is a cross-sectional view showing a schematic configuration of acathode material 1000 in the first embodiment.

The cathode material 1000 according to the first embodiment includessecond solid electrolyte particles 100, cathode active materialparticles 110, and a coating layer 111.

The cathode active material particles 110 and the second solidelectrolyte particles 100 are separated by the coating layer 111 and arenot in direct contact with each other.

The coating layer 111 is a layer including the first solid electrolytematerial. In other words, the coating layer 111 is provided on thesurface of the cathode active material particles 110.

The thickness of the coating layer 111 may be not less than 1 nm and notmore than 100 nm.

If the thickness of the coating layer 111 is not less than 1 nm, thedirect contact between the cathode active material particles 110 and thesecond solid electrolyte particles 100 can be suppressed, and a sidereaction of the second solid electrolyte material can be suppressed. Asa result, the charge/discharge efficiency can be improved.

In addition, the thickness of the coating layer 111 does not excessivelyincrease since the thickness of the coating layer 111 is not more than100 nm. As a result, the internal resistance of the battery can besufficiently lowered. As a result, the energy density of the battery canbe increased.

In addition, the coating layer 111 may uniformly coat the cathode activematerial particles 110. The direct contact between the cathode activematerial particles 110 and the second solid electrolyte particles 100can be suppressed, and the side reaction of the second solid electrolytematerial can be suppressed. As a result, the charge/dischargecharacteristic of the battery can be further improved, and the increasein the reaction overvoltage of the battery can be suppressed.

Alternatively, the coating layer 111 may coat a part of the cathodeactive material particles 110. The plurality of the cathode activematerial particles 110 are in direct contact with each other through thepart that does not have the coating layer 111 to improve the electronconductivity between the cathode active material particles 110. As aresult, the battery is allowed to operate at a high output.

In addition, the shape of the second solid electrolyte material in thefirst embodiment is not particularly limited, and may be, for example, aneedle shape, a spherical shape, or an elliptical spherical shape. Forexample, the shape of the second solid electrolyte material may beparticles.

For example, if the shape of the second solid electrolyte material inthe first embodiment is particulate (for example, spherical), the mediandiameter may be not more than 100 μm. If the median diameter is not morethan 100 μm, a good dispersion state of the cathode active materialparticles 110 and the second solid electrolyte particles 100 can beformed in the cathode material. As a result, the charge/dischargecharacteristic is improved. In the first embodiment, the median diametermay be not more than 10 μm.

According to the above configuration, in the cathode material, the gooddispersion state of the cathode active material particles 110 and thesecond solid electrolyte particles 100 can be formed.

In the first embodiment, the second solid electrolyte particles 100 maybe smaller than the median diameter of the cathode active materialparticles 110.

According to the above configuration, a better dispersion state of thesecond solid electrolyte particles 100 and the cathode active materialparticles 110 can be formed in the electrode.

The median diameter of the cathode active material particles 110 may benot less than 0.1 μm and not more than 100 μm.

If the median diameter of the cathode active material particles 110 isnot less than 0.1 μm, in the cathode material 1000, the good dispersionstate of the cathode active material particles 110 and the second solidelectrolyte particles 100 can be formed. As a result, thecharge/discharge characteristic of the battery is improved.

In addition, if the median diameter of the cathode active materialparticles 110 is not more than 100 μm, lithium diffusion in the cathodeactive material particles 110 is accelerated. As a result, the batterycan operate at a high output.

The median diameter of the cathode active material particles 110 may belarger than the median diameter of the second solid electrolyteparticles 100. Thereby, a good dispersion state of the cathode activematerial particles 110 and the second solid electrolyte particles 100can be formed.

In the cathode material 1000 according to the first embodiment, thesecond solid electrolyte particles 100 and the coating layer 111 may bein contact with each other as shown in FIG. 1. In this case, the coatinglayer 111 and the cathode active material particles 110 are in contactwith each other.

In addition, the cathode material 1000 in the first embodiment mayinclude a plurality of the second solid electrolyte particles 100 and aplurality of the cathode active material particles 110.

In addition, the content of the second solid electrolyte particles 100and the content of the cathode active material particles 110 in thecathode material 1000 in the first embodiment may be the same as ordifferent from each other.

<Manufacturing Method of First Solid Electrolyte Material and SecondSolid Electrolyte Material>

The first solid electrolyte material and the second solid electrolytematerial in the first embodiment may be manufactured by the followingmethod, for example.

Binary halide raw material powders are prepared so as to provide ablending ratio of a target composition. For example, if Li₃YCl₆ isproduced, LiCl and YCl₃ are prepared at a molar ratio of 3:1.

At this time, “M”, “Me”, and “X” in the above composition formula can bedetermined by selecting the kinds of the raw material powders. Inaddition, by adjusting the raw materials, the blending ratio, and thesynthesis process, the values “α”, “β,” “γ”, “d”, “δ”, “a”, “x”, and “y”can be adjusted.

The raw material powders are mixed well, and then the raw materialpowders are mixed and ground to react using a mechanochemical millingmethod. Alternatively, the raw material powders may be mixed well, andthen sintered in a vacuum.

Thereby, the solid electrolyte material including the crystal phasedescribed above is provided.

In addition, the structure (namely, the crystal structure) of thecrystal phase in the solid electrolyte material can be determined byadjusting the reaction method and reaction conditions of the rawmaterial powders.

Second Embodiment

Hereinafter, the second embodiment will be described. The descriptionwhich has been set forth in the above-described first embodiment isomitted as appropriate.

FIG. 2 is a cross-sectional view showing a schematic configuration of abattery 2000 in the second embodiment.

The battery 2000 in the second embodiment comprises a cathode 201, anelectrolyte layer 202, and an anode 203.

The cathode 201 includes the cathode material (for example, the cathodematerial 1000) in the first embodiment.

The electrolyte layer 202 is disposed between the cathode 201 and theanode 203.

According to the above configuration, the increase in the reactionovervoltage of the battery can be suppressed.

With regard to a volume ratio “v: 100-v” of the cathode active materialparticles 110 and the second solid electrolyte particles 100 included inthe cathode 201, 30≤v≤95 may be satisfied. If 30≤v, a sufficient batteryenergy density can be secured. In addition, if v≤95, the operation at ahigh output can be realized.

The thickness of the cathode 201 may be not less than 10 μm and not morethan 500 μm. In addition, if the thickness of the cathode 201 is notless than 10 μm, a sufficient battery energy density can be secured. Inaddition, if the thickness of the cathode 201 is not more than 500 μm,the operation at a high output can be realized.

The electrolyte layer 202 is a layer including an electrolyte material.The electrolyte material is, for example, a solid electrolyte material(namely, a third solid electrolyte material). In other words, theelectrolyte layer 202 may be a solid electrolyte layer.

As the third solid electrolyte material included in the electrolytelayer 202, a halide solid electrolyte, a sulfide solid electrolyte, anoxide solid electrolyte, a polymer solid electrolyte, or a complexhydride solid electrolyte may be used.

As the halide solid electrolyte of the third solid electrolyte material,the same halide solid electrolyte as the first solid electrolytematerial and/or the second solid electrolyte material in the firstembodiment may be used. In other words, the electrolyte layer 202 mayinclude the same halide solid electrolyte as the first solid electrolytematerial and/or the second solid electrolyte material in the firstembodiment.

According to the above configuration, the output density and thecharge/discharge characteristic of the battery can be further improved.

Further, the third solid electrolyte material included in theelectrolyte layer 202 may be a halide solid electrolyte different fromthe first solid electrolyte material and the second solid electrolytematerial in the first embodiment. In other words, the electrolyte layer202 may include a halide solid electrolyte different from the firstsolid electrolyte material and the second solid electrolyte material inthe first embodiment.

According to the above configuration, the charge/dischargecharacteristic of the battery can be further improved.

As the sulfide solid electrolyte of the third solid electrolytematerial, Li₂S—P₂S₅, Li₂S—SiS₂, Li₂S—B₂S₃, Li₂S—GeS₂,Li_(3.25)Ge_(0.25)P_(0.75)S₄, or Li₁₀GeP₂S₁₂ can be used. In addition,LiX, Li₂O, MO_(q), or LipMO_(q) may be added thereto. Here, X is one ormore kinds of elements selected from the group consisting of F, Cl, Br,and I. M is one or more kinds of elements selected from the groupconsisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. In addition, p and qare each independently a natural number.

Alternatively, the same sulfide solid electrolyte as the second solidelectrolyte material in the first embodiment may be used as the sulfidesolid electrolyte of the third solid electrolyte material. In otherwords, the electrolyte layer 202 may include the same sulfide solidelectrolyte as the second solid electrolyte material in the firstembodiment.

According to the above configuration, since the sulfide solidelectrolyte excellent in reduction stability is included, a lowpotential anode material such as graphite or metallic lithium can beused, and the energy density of the battery can be improved. Inaddition, according to the configuration in which the electrolyte layer202 includes the same sulfide solid electrolyte as the second solidelectrolyte material in the first embodiment, the charge/dischargecharacteristic of the battery can be improved.

As the oxide solid electrolyte of the third solid electrolyte material,for example, a NASICON solid electrolyte such as LiTi₂(PO₄)₃ and theelement substitution products thereof, a (LaLi)TiO₃ perovskite solidelectrolyte, a LISICON solid electrolyte such as Li₁₄ZnGe₄O₁₆, Li₄SiO₄,LiGeO₄ and the element substitution products thereof, a garnet solidelectrolyte such as Li₇La₃Zr₂O₁₂ and the element substitution productsthereof, Li₃N and the H substitution products thereof, Li₃PO₄ and the Nsubstitution products thereof, glass to which Li₂SO₄ or Li₂CO₃ has beenadded using a Li—Bi—O compound such as LiBO₂ or Li₃BO₃ as a base, orglass ceramics may be used.

As the polymer solid electrolyte of the third solid electrolytematerial, for example, a compound of a polymer compound and a lithiumsalt can be used. The polymer compound may have an ethylene oxidestructure. Due to the ethylene oxide structure, a large amount oflithium salt can be included, and the ion conductivity can be furtherincreased. As the lithium salt, LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiSO₃CF₃,LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiN(SO₂CF₃)(SO₂C₄F₉), or LiC(SO₂CF₃)₃ maybe used. As the lithium salt, one lithium salt selected from these maybe used alone. Alternatively, a mixture of two or more lithium saltsselected from these may be used as the lithium salt.

As the complex hydride solid electrolyte of the third solid electrolytematerial, for example, LiBH₄—LiI or LiBH₄—P₂S₅ may be used.

The solid electrolyte layer may include a third solid electrolytematerial as a main component. In other words, the solid electrolytelayer may include the third solid electrolyte material, for example, ata weight ratio of not less than 50% (namely, 50% by weight or more) withrespect to the entire solid electrolyte layer.

According to the above configuration, the charge/dischargecharacteristic of the battery can be further improved.

In addition, the solid electrolyte layer may include the third solidelectrolyte material, for example, at a weight ratio of not less than70% (namely, 70% by weight or more) with respect to the entire solidelectrolyte layer.

According to the above configuration, the charge/dischargecharacteristic of the battery can be further improved.

The solid electrolyte layer includes the third solid electrolytematerial as the main component thereof, and the solid electrolyte layermay further include inevitable impurities. The solid electrolyte layermay include the starting materials used for the synthesis of the thirdsolid electrolyte material. The solid electrolyte layer may includeby-products or decomposition products generated when the solidelectrolyte material is synthesized.

In addition, the solid electrolyte layer may include the third solidelectrolyte material, for example, at a weight ratio of 100% (namely,100% by weight) with respect to the entire electrolyte layer, except forthe inevitable impurities.

According to the above configuration, the charge/dischargecharacteristic of the battery can be further improved.

The solid electrolyte layer may be comprised only from the third solidelectrolyte material.

The solid electrolyte layer may include two or more kinds of thematerials listed as the third solid electrolyte material. For example,the solid electrolyte layer may include the halide solid electrolyte andthe sulfide solid electrolyte.

The thickness of the electrolyte layer 202 may be not less than 1 μm andnot more than 300 μm. If the thickness of the electrolyte layer 202 isnot less than 1 μm, the cathode 201 and the anode 203 are easilyseparated. In addition, if the thickness of the electrolyte layer 202 isnot more than 300 μm, the operation at a high output can be realized.

The anode 203 includes a material having a property of occluding andreleasing metal ions (for example, lithium ions). The anode 203includes, for example, an anode active material.

As the anode active material, a metal material, a carbon material, anoxide, a nitride, a tin compound, or a silicon compound may be used. Themetal material may be a single metal. Alternatively, the metal materialmay be an alloy. Examples of the metal material include a lithium metaland a lithium alloy. Examples of the carbon material include naturalgraphite, coke, graphitized carbon, carbon fiber, spherical carbon,artificial graphite, and amorphous carbon. From the viewpoint ofcapacity density, silicon (Si), tin (Sn), a silicon compound, or a tincompound may be used.

The anode 203 may include a solid electrolyte material. As the solidelectrolyte material, the solid electrolyte material exemplified as thematerial forming the electrolyte layer 202 may be used. According to theabove configuration, the lithium ion conductivity inside the anode 203is increased, and the operation at a high output can be realized.

The median diameter of the anode active material particles may be notless than 0.1 μm and not more than 100 μm. If the median diameter of theanode active material particles is not less than 0.1 μm, a gooddispersion state of the anode active material particles and the solidelectrolyte material can be formed in the anode. Thereby, thecharge/discharge characteristic of the battery is improved. In addition,if the median diameter of the anode active material particles is notmore than 100 μm, lithium diffusion in the anode active materialparticles is accelerated. As a result, the battery can operate at a highoutput.

The median diameter of the anode active material particles may be largerthan the median diameter of the solid electrolyte material. Thereby, agood dispersion state of the anode active material particles and thesolid electrolyte material can be formed.

With regard to a volume ratio “v: 100-v” of the anode active materialparticles and the solid electrolyte material included in the anode 203,30≤v≤95 may be satisfied. If 30≤v, a sufficient battery energy densitycan be secured. In addition, if v≤95, the operation at a high output canbe realized.

The thickness of the anode 203 may be not less than 10 μm and not morethan 500 μm. If the thickness of the anode is not less than 10 μm, asufficient battery energy density can be secured. In addition, if thethickness of the anode is not more than 500 μm, the operation at a highoutput can be realized.

At least one of the cathode 201, the electrolyte layer 202, and theanode 203 may include a binder for the purpose of improving the adhesionbetween the particles. The binder is used to improve the bindingproperty of the material forming the electrode. An example of the binderis poly(vinylidene fluoride), polytetrafluoroethylene, polyethylene,polypropylene, aramid resin, polyamide, polyimide, polyamideimide,polyacrylonitrile, polyacrylic acid, methyl polyacrylate ester, ethylpolyacrylate ester, hexyl polyacrylate ester, polymethacrylic acid,methyl polymethacrylate ester, ethyl polymethacrylate ester, hexylpolymethacrylate ester, polyvinyl acetate, polyvinylpyrrolidone,polyether, polyethersulfone, hexafluoropolypropylene, styrene butadienerubber, or carboxymethylcellulose. As the binder, a copolymer of two ormore kinds of materials selected from tetrafluoroethylene,hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether,vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene,pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, andhexadiene may be used. In addition, two or more kinds of materialsselected from these may be mixed and used as a binder.

In addition, at least one of the cathode 201 and the anode 203 mayinclude a conductive assistant for the purpose of improving electronconductivity. Examples of the conductive assistant include graphite suchas natural graphite or artificial graphite; carbon black such asacetylene black or ketjen black; a conductive fiber such as a carbonfiber or a metal fiber; carbon fluoride; metal powder such as aluminum;conductive whiskers such as zinc oxide or potassium titanate; aconductive metal oxide such as titanium oxide; or a conductive polymercompound such as polyaniline, polypyrrole, or polythiophene. Costreduction can be achieved by using a carbon conductive assistant.

An example of the shape of the battery in the second embodiment may be acoin, a cylinder, a prism, a sheet, a button, a flat type, or a stackingstructure.

EXAMPLES

Hereinafter, details of the present disclosure will be described withreference to inventive examples and comparative examples.

Inventive Example 1

[Production of Second Solid Electrolyte Material]

In an argon glove box with a dew point of −60° C. or less, raw materialpowders LiBr, LiCl, LiI, YCl, and YBr₃ were prepared at a molar ratio ofLiBr:LiCl:LiI:YC₃:YBr₃=1:1:4:1:1. Subsequently, milling processing wasperformed at 600 rpm for 25 hours using a planetary ball mill(manufactured by Fritsch, type P-7) to provide a powder of the secondsolid electrolyte material Li₃YBr₂Cl₂I₂.

[Production of Cathode Active Material Coating Layer]

In an argon glove box with a dew point of −60° C. or less, raw materialpowders LiCl and YCl₃ were prepared at a molar ratio ofLiCl:YCl₃=2.7:1.1. Subsequently, milling processing was performed at 600rpm for 25 hours using a planetary ball mill (manufactured by Fritsch,type P-5) to provide a powder of the first solid electrolyte materialLi_(2.7)Y_(1.1)Cl₆. The material of the coating layer is a first solidelectrolyte material.

Mixing with an agate mortar was used to form a Li_(2.7)Y_(1.1)Cl₆coating layer on the cathode active material Li(NiCoMn)O₂ (hereinafter,referred to as NCM). The first solid electrolyte material(Li_(2.7)Y_(1.1)Cl₆) and the cathode active material (NCM) were preparedat a weight ratio of 1:10 in an argon glove box. By mixing these with anagate mortar, the coated cathode active material of the inventiveexample 1 in which the coating layer was formed on the surface of eachof the particles was provided.

[Production of Cathode Material]

In the argon glove box, the second solid electrolyte material of theinventive example 1 and the coated cathode active material of theinventive example 1 were prepared at a weight ratio of 23:77. By mixingthese in an agate mortar, the cathode material of the inventive example1 was produced.

Inventive Example 2

[Production of Cathode Active Material Coating Layer]

In an argon glove box with a dew point of −60° C. or less, raw materialpowders LiBr and YBr₃ were prepared at a molar ratio of LiBr:YBr₃=3:1.Subsequently, milling processing was performed at 600 rpm for 25 hoursusing a planetary ball mill (manufactured by Fritsch, type P-7) toprovide a powder of the first solid electrolyte material Li₃YBr₆.

The same steps as those of the inventive example 1 were performed toprovide the cathode material of the inventive example 2, except for theproduction of the cathode active material coating layer.

Inventive Example 3

[Production of Cathode Active Material Coating Layer]

In an argon glove box with a dew point of −60° C. or less, raw materialpowders LiCl, YCl₃, and ZrCl₄ were prepared at a molar ratio ofLiCl:YCl₃:ZrCl₄=5:1:1. Subsequently, milling processing was performed at600 rpm for 25 hours using a planetary ball mill (manufactured byFritsch, type P-7) to provide a powder of the first solid electrolytematerial Li_(2.5)Y_(0.5)Zr_(0.5)Cl₆.

The same steps as those of the inventive example 1 were performed toprovide the cathode material of the inventive example 3, except for theproduction of the cathode active material coating layer.

Comparative Example 1

The same steps as those of the inventive example 1 were performed toprovide the cathode material of the comparative example 1, except thatthe cathode active material coating layer was not produced and that NCMhaving a surface on which the coating layer was not formed was used.

[Production of Sulfide Solid Electrolyte]

In an argon glove box with a dew point of −60° C. or less, Li₂S and P₂S₅were prepared at a molar ratio of Li₂S:P₂S₅=75:25. These were ground andmixed in a mortar. Then, milling processing was performed at 510 rpm for10 hours using a planetary ball mill (manufactured by Fritsch, type P-7)to provide a glassy solid electrolyte. The glassy solid electrolyte washeat-treated at 270° C. for two hours in an inert atmosphere. In thisway, Li₂S—P₂S₅, which was a glass ceramic solid electrolyte, wasprovided.

[Production of Battery]

The following steps were performed, using each of the cathode materialsof the inventive examples 1 to 3 and the comparative example 1 and theglass ceramic Li₂S—P₂S₅.

First, in an insulating outer cylinder, 80 mg of Li₂S—P₂S₅ and 10 mg ofthe cathode material were stacked in this order. This waspressure-molded at a pressure of 360 MPa to provide a cathode and asolid electrolyte layer.

Next, a metal In (thickness: 200 μm) was stacked on the cathode to forma cathode current collector.

Next, a metal In (thickness 200 μm), a metal Li (thickness 300 μm), anda metal In (thickness 200 μm) were stacked in this order on the surfaceof the solid electrolyte layer opposite to the other surface which wasin contact with the cathode. This was pressure-molded at a pressure of80 MPa to produce a stacking structure composed of the cathode, thesolid electrolyte layer, and an anode.

Next, stainless steel current collectors were placed on the upper andlower parts of the stacking structure, and current collector leads wereattached to the current collectors.

Finally, an insulating ferrule was used to block and seal the inside ofthe insulating outer cylinder from the outside atmosphere to produce abattery.

In this way, the batteries of the inventive examples 1 to 3 and thecomparative example 1 were produced.

[Charge Test]

Using each of the batteries of the inventive examples 1 to 3 and thecomparative example 1, a charge test was performed under the followingconditions.

The battery was placed in a constant temperature chamber at 25° C.

The battery was charged with a constant current at a current value of 70μA at a 0.05C rate (20 hour rate) with respect to the theoreticalcapacity of the battery. The charge was terminated at a voltage of 3.7V.

As described above, the increase in voltage from an OCV voltage (i.e.,3.084 V) at the capacity of 50 mAh/g (converted to the weight of thecathode active material) of each of the batteries of the inventiveexamples 1 to 3 and the comparative example 1 was defined as anovervoltage. The results are shown in Table 1 below.

TABLE 1 First solid electrolyte material Second solid Overvoltage(coating material) electrolyte material during charge* InventiveLi_(2.7)Y_(1.1)Cl₆ Li₃YBr₂Cl₂I₂ 44 mV Example 1 Inventive Li₃YBr₆Li₃YBr₂Cl₂I₂ 17 mV Example 2 Inventive Li_(2.5)Y_(0.5)Zr_(0.5)Cl₆Li₃YBr₂Cl₂I₂ 43 mV Example 3 Comparative None Li₃YBr₂Cl₂I₂ 213 mV Example 1 *Increase in voltage from an OCV voltage (3.084 V) at thecharge capacity of 50 mAh/g.

<<Discussion>>

From the results of the inventive example 1 and the comparative example1 shown in Table 1, in the battery using the halide solid electrolyteincluding iodine (one example of the second solid electrolyte material)for the cathode, it was confirmed that the increase in the overvoltageof the battery was suppressed by providing the coating layer includingthe first solid electrolyte material on the surface of the cathodeactive material. Here, the first solid electrolyte material included inthe battery is represented by the composition formula Li_(α)M_(β)X_(γ).The values of α, β, and γ are each independently a value greater than 0,M includes at least one element selected from the group consisting ofmetalloid elements and metal elements other than Li, and X includes atleast one element selected from the group consisting of Cl and Br.

From the result of the comparative example 1 shown in Table 1, it hasbeen confirmed that, if the halide solid electrolyte including iodine isused for the cathode and no coating layer including the first solidelectrolyte material is provided, the overvoltage during the charge is ahigh value of 213 mV.

In addition, from the results of the inventive examples 1 to 3 and thecomparative example 1, it has been confirmed that, even if the firstsolid electrolyte material used for the coating layer has differentcompositions and structures, the oxidative decomposition of the secondsolid electrolyte material in the electrode is suppressed. It has beenconfirmed that, with the oxidative decomposition, the increase in theovervoltage of the battery can be suppressed.

Inventive Example 4

[Production of Second Solid Electrolyte Material]

In an argon glove box with a dew point of −60° C. or less, Li₂S and P₂S₅were prepared at a molar ratio of Li₂S:P₂S₅=75:25. These were ground andmixed in a mortar. Then, milling processing was performed at 510 rpm for10 hours using a planetary ball mill (manufactured by Fritsch, type P-7)to provide a glassy solid electrolyte. The glassy solid electrolyte washeat-treated at 270° C. for two hours in an inert atmosphere. In thisway, Li₂S—P₂S₅, which was a glass ceramic second solid electrolytematerial, was provided.

[Production of Cathode Active Material Coating Layer]

In an argon glove box with a dew point of −60° C. or less, raw materialpowders LiCl and YCl₃ were prepared at a molar ratio ofLiCl:YCl₃=2.7:1.1. Subsequently, milling processing was performed at 600rpm for 25 hours using a planetary ball mill (manufactured by Fritsch,type P-5) to provide a powder of the first solid electrolyte materialLi_(2.7)Y_(1.1)Cl₆. The material of the coating layer is a first solidelectrolyte material.

Mixing with an agate mortar was used to form the Li_(2.7)Y_(1.1)Cl₆coating layer on the cathode active material Li(NiCoMn)O₂ (hereinafter,referred to as NCM). The first solid electrolyte material(Li_(2.7)Y_(1.1)Cl₆) and the cathode active material (NCM) were preparedat a weight ratio of 1:10 in an argon glove box. By mixing these with anagate mortar, the coated cathode active material of the inventiveexample 4 in which the coating layer was formed on the surface of eachof the particles was provided. In other words, a coating layer wasformed on at least a part of a surface of each of all or some of theplurality of particles of the cathode active material.

[Production of Cathode Material]

In the argon glove box, the second solid electrolyte material of theinventive example 4 and the coated cathode active material of theinventive example 4 were prepared at a weight ratio of 23:77. By mixingthese in an agate mortar, the cathode material of the inventive example4 was produced.

Inventive Example 5

[Production of Cathode Active Material Coating Layer]

In an argon glove box with a dew point of −60° C. or less, raw materialpowders LiBr and YBr₃ were prepared at a molar ratio of LiBr:YBr₃=3:1.Subsequently, milling processing was performed at 600 rpm for 25 hoursusing a planetary ball mill (manufactured by Fritsch, type P-7) toprovide a powder of the first solid electrolyte material Li₃YBr₆.

The same steps as those of the inventive example 4 were performed toprovide the cathode material of the inventive example 5, except for theproduction of the cathode active material coating layer.

Inventive Example 6

[Production of Cathode Active Material Coating Layer]

In an argon glove box with a dew point of −60° C. or less, raw materialpowders LiCl, YCl, ZrCl₄ were prepared at a molar ratio ofLiCl:YCl₃:ZrCl₄=5:1:1. Subsequently, milling processing was performed at600 rpm for 25 hours using a planetary ball mill (manufactured byFritsch, type P-7) to provide a powder of the first solid electrolytematerial Li_(2.5)Y_(0.5)Zr_(0.5)Cl₆.

The same steps as those of the inventive example 4 were performed toprovide the cathode material of the inventive example 6, except for theproduction of the cathode active material coating layer.

Comparative Example 2

The same steps as those of the inventive example 4 were performed toprovide the cathode material of the comparative example 2, except thatthe cathode active material coating layer was not produced and that NCMhaving a surface on which the coating layer was not formed was used.

Comparative Example 3

[Production of Second Solid Electrolyte Material]

In an argon glove box with a dew point of −60° C. or less, raw materialpowders LiBr, LiCl, LiI, YCl₃, and YBr₃ were prepared at a molar ratioof LiBr:LiCl:LiI:YCl₃:YBr₃=1:1:4:1:1. Subsequently, milling processingwas performed at 600 rpm for 25 hours using a planetary ball mill(manufactured by Fritsch, type P-7) to provide a powder of the secondsolid electrolyte material Li₃YBr₂Cl₂I₂.

The same steps as those of the inventive example 4 were performed toprovide the cathode material of the comparative example 3, except thatthe cathode active material coating layer was not produced and that NCMhaving a surface on which the coating layer was not formed was used, andexcept for the production of the second solid electrolyte material.

[Production of Battery]

The following steps were performed using each of the cathode materialsof the inventive examples 4 to 6 and the comparative examples 2 to 3 andLi₂S—P₂S₅ in the form of the glass ceramics.

First, in an insulating outer cylinder, 80 mg of Li₂S—P₂S₅ and 10 mg ofthe cathode material were stacked in this order. This waspressure-molded at a pressure of 360 MPa to provide a cathode and asolid electrolyte layer. Next, a metal In (thickness: 200 μm) wasstacked on the cathode to form a cathode current collector. Next, ametal In (thickness 200 μm), a metal Li (thickness 300 μm), and a metalIn (thickness 200 μm) were stacked in this order on the surface of thesolid electrolyte layer opposite to the other surface which was incontact with the cathode. This was pressure-molded at a pressure of 80MPa to produce a stacking structure composed of the cathode, the solidelectrolyte layer, and an anode.

Next, stainless steel current collectors were placed on the upper andlower parts of the stacking structure, and current collector leads wereattached to the current collectors.

Finally, an insulating ferrule was used to block and seal the inside ofthe insulating outer cylinder from the outside atmosphere to produce abattery.

As described above, the batteries of the inventive examples 4 to 6 andthe comparative examples 2 to 3 were produced.

[Charge Test]

Using each of the batteries of the inventive examples 4 to 6 and thecomparative examples 2 to 3, a charge test was performed under thefollowing conditions.

The battery was placed in a constant temperature chamber at 25° C.

The battery was charged with a constant current at a current value of 70μA at a 0.05C rate (20 hour rate) with respect to the theoreticalcapacity of the battery. The charge was (terminated at a voltage of3.7V. The battery was left at rest for twenty minutes in an opencircuit, and then a stabilized open circuit voltage was read. Thedifference between the open circuit voltage and the end voltage 3.7V wasdefined as an overvoltage.

As described above, the overvoltage of each of the inventive examples 4to 6 and the comparative examples 2 to 3 was provided. The results areshown in the following Table 2.

TABLE 2 First solid electrolyte material Second solid Overvoltage(coating material) electrolyte material during charge* InventiveLi_(2.7)Y_(1.1)Cl₆ Li₂S—P₂S₅ 46 mV Example 4 Inventive Li₃YBr₆ Li₂S—P₂S₅65 mV Example 5 Inventive Li_(2.5)Y_(0.5)Zr_(0.5)Cl₆ Li₂S—P₂S₅ 78 mVExample 6 Comparative None Li₂S—P₂S₅ 131 mV Example 1 Comparative NoneLi₃YBr₂Cl₂I₂ 186 mV Example 2 *Dropped voltage during quiescentoperation after charge

<<Discussion>>

From the results shown in Table 2, it has been confirmed that, in thebattery using the sulfide solid electrolyte (one example of the secondsolid electrolyte material) for the cathode, the increase in theovervoltage of the battery can be suppressed by providing the coatinglayer including the first solid electrolyte material on the surface ofthe cathode active material. Here, the first solid electrolyte materialincluded in the battery is represented by a composition formulaLi_(α)M_(β)X_(γ). The values of α, β, and γ are each independently avalue greater than 0, M includes at least one element selected from thegroup consisting of metalloid elements and metal elements other than Li,and X includes at least one element selected from the group consistingof Cl and Br.

From the results of the comparative example 2 shown in Table 2, it hasbeen confirmed that, if the sulfide solid electrolyte is used for thecathode and the coating layer including the first solid electrolytematerial is not provided, the overvoltage at the end of the charge is ahigh value of 131 mV.

In addition, from the results of the inventive examples 4 to 6 and thecomparative example 2, it has been confirmed that even if the firstsolid electrolyte material used for the coating layer has differentcompositions and structures, the oxidative decomposition of the secondsolid electrolyte material in an electrode is suppressed. It has beenconfirmed that, with the oxidative decomposition, the increase in theovervoltage of the battery can be suppressed.

In addition, from the result of the comparative example 3, it has beenconfirmed that, if the cathode active material and the halide solidelectrolyte including iodine are in direct contact, the overvoltage atthe end of the charge is a high value of 186 mV. This is presumablybecause iodine was oxidized to form a resistance layer. On the otherhand, from the results of the inventive examples 4 to 6, it has beenconfirmed that the formation of the high resistance layer due to thecontact between the cathode active material and the sulfide solidelectrolyte can be suppressed by coating the cathode active materialwith the halide solid electrolyte which does not include iodine.

INDUSTRIAL APPLICABILITY

The battery of the present disclosure can be used, for example, as anall-solid lithium secondary battery.

REFERENTIAL SIGNS LIST

-   1000 Cathode material-   100 Second solid electrolyte particle-   110 Cathode active material particle-   111 Coating layer-   2000 Battery-   201 Cathode-   202 Electrolyte layer-   203 Anode

1. A cathode material, comprising: a cathode active material; a coatinglayer which coats at least a part of a surface of the cathode activematerial and includes a first solid electrolyte material; and a secondsolid electrolyte material, wherein the first solid electrolyte materialincludes Li, M, and X; the first solid electrolyte material does notinclude sulfur; M includes at least one element selected from the groupconsisting of metalloid elements and metal elements other than Li; and Xincludes at least one element selected from the group consisting of Cland Br.
 2. The cathode material according to claim 1, wherein the firstsolid electrolyte material is represented by the following compositionformula (1):Li_(α)M_(β)X_(γ)  Formula (1) where α, β, and γ are each independently avalue greater than 0; M is at least one element selected from the groupconsisting of metalloid elements and metal elements other than Li; and Xis at least one element selected from the group consisting of Cl and Br.3. The cathode material according to claim 2, wherein M includesyttrium.
 4. The cathode material according to claim 3, wherein 2.5≤α≤3,1≤β≤1.1, and γ=6 are satisfied.
 5. The cathode material according toclaim 1, wherein the second solid electrolyte material is represented bythe following composition formula (2):Li_(α′)M_(β′)X_(γ′)  Formula (2) where α′, β′, and γ′ are eachindependently a value greater than 0, M′ includes at least one elementselected from the group consisting of metalloid elements and metalelements other than Li; and X′ includes I and at least one elementselected from the group consisting of C and Br.
 6. The cathode materialaccording to claim 5, wherein M′ includes yttrium.
 7. The cathodematerial according to claim 5, wherein X′ includes Cl and Br.
 8. Thecathode material according to claim 1, wherein the second solidelectrolyte material is a sulfide solid electrolyte.
 9. The cathodematerial according to claim 8, wherein the sulfide solid electrolyte islithium sulfide and phosphorus sulfide.
 10. The cathode materialaccording to claim 8, wherein the sulfide solid electrolyte isLi₂S—P₂S₅.
 11. The cathode material according to claim 10, wherein thecathode active material is a lithium nickel-cobalt-manganese oxide. 12.A battery, comprising: a cathode including the cathode materialaccording to claim 1; an anode; and an electrolyte layer providedbetween the cathode and the anode.
 13. The battery according to claim12, wherein the electrolyte layer includes the same material as at leastone of the first solid electrolyte material and the second solidelectrolyte material.
 14. The battery according to claim 13, wherein theelectrolyte layer includes the same material as the first solidelectrolyte material.
 15. The battery according to claim 12, wherein theelectrolyte layer includes a halide solid electrolyte different from thefirst solid electrolyte material.
 16. The battery according to claim 12,wherein the electrolyte layer includes a halide solid electrolytedifferent from the first solid electrolyte material and the second solidelectrolyte material.
 17. The battery according to claim 12, wherein theelectrolyte layer includes a sulfide solid electrolyte.
 18. The cathodematerial according to claim 1, wherein the first solid electrolytematerial is a halide which does not include iodine; the second solidelectrolyte material is a halide which includes a sulfide or iodine; andthe cathode active material and the second solid electrolyte materialare separated by the first solid electrolyte material and are not indirect contact with each other.
 19. The battery according to claim 12,wherein the first solid electrolyte material is a halide which does notinclude iodine; the second solid electrolyte material is a halide whichincludes a sulfide or iodine; and the cathode active material and thesecond solid electrolyte material are separated by the first solidelectrolyte material and are not in direct contact with each other.